The invention relates to a method for operating a drive device of a vehicle, in particular a motor vehicle, which has at least one electric or hydraulic machine as a drive unit. In addition, the invention relates to a corresponding device and to a system.
Modern motor vehicle drive trains usually do not have direct measurement of currently generated drive torques for reasons of cost. The torque output or power output of a drive unit therefore cannot be determined directly. In particular in the case of hybrid vehicles or electric vehicles whose drive devices have at least one electric or hydraulic machine as a drive unit, in particular in addition to a conventional internal combustion engine, there can be frictional engagement between one or more of these drive units and the driven wheels of the motor vehicle even in the case of a stationary vehicle. A faulty torque output or power output of the at least one drive unit, for example owing to a communication error or a software error or fault in an on-board component, can cause a safety-critical incorrect movement of the vehicle. In the case of vehicles with an electric or hydraulic machine as a drive unit, a reverse gear speed in the transmission is frequently dispensed with if such a reverse gear speed is provided at all. If a reverse gear speed is desired in this case, a change of direction of rotation of the drive unit takes place compared to the direction of rotation in the case of forward travel. The change in the direction of rotation is brought about by a changed actuation, for example by a changed direction of rotation of the magnetic field of a three-phase machine which is provided as a drive unit. In addition to component faults or software errors, faults in the power cabling, the sensor cables of a rotor position sensor or rotational speed sensor or incorrect orientation of sensor components relative to the shaft or to the housing of the drive unit can lead to a torque which acts in the wrong direction. When the vehicle starts, this would lead to a vehicle movement in the wrong direction of travel. In particular if persons are located in the vicinity of the vehicle, this results in a situation which is extremely safety-critical.